1.

In the determination of hardness of a sample of water, the following results were obtained: Volume of sample of `H_2O=100mL` Volume of `(N)/(50)Na_2CO_3` added to it `=20mL` Volume of `(N)/(50)H_2SO_4` used to back titrate the unreacted `Na_2CO_3=10mL` Calculate the hardness of water in g `L^(-1)`

Answer» m" Eq of "unreacted `Na_(2)CO_(3)=m" Eq of "H_(2)SO_(4)`
`=(1xx10)/(50)=(1)/(5)`
Total m" Eq of "`Na_(2)CO_(3)` taken `=(1xx20)/(50)=(2)/(5)`
m" Eq of "`Na_(2)CO_(3)` absorbed by `H_(2)O=(2)/(5)-(1)/(5)=(1)/(5)`
Weight of `Na_(2)CO_(3)` absorbed by `H_(2)O`
`=(1)/(5)xx10^(-3)xx53g (Ew_(Na_(2)CO_(3))=53`
`=0.0106 g ((Na_(2)CO_(3))/(100mL)) of H_(2)O`
`=(100xx0.0106)/(106)g of CaCO_(3)`
`=0.01 g of CaCO_(3)`
`=(0.1xx1000)/(100)"g of "((CaCO_(3))/(LH_(2)O))`
`=0.1g" of "(CaCO_(3))/(L)" of "H_(2)O`


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